The Effects of a Parametric Variation of the Rim Seal Geometry on the Interaction Between Hub Leakage and Mainstream Flows in High Pressure Turbines

Abstract

The objective ofthis work was to assess and understand the effects of a parametric variation performed on a typical overlapping rim seal geometry. The datum geometry has been the focus of a detailed experimental investigation employing a large-scale linear cascade subjected to a range of the mass flow rates and swirl velocities of the leakage air. The parametric variations described in this paper were examined using validated computational fluid dynamics (CFD). As a part of the parametric studies, both the axial and the radial seal clearance between the rotor fin (angel wing) and stator platform were varied as well as the length of the overlap between stator and rotor platforms. In addition, the effects of forward and backward facing annulus steps were also investigated. It has been found that a backward-facing annulus step was detrimental for all conditions considered, while a forward-facing step offered improvements for smaller step heights and/or lower leakage fractions. Tightening of the seal clearances closer to the annulus line improved the sealing effectiveness but often at the expense of increased losses. On the other hand, increasing the overlap length led to improvements in the sealing effectiveness with very small effects on the overall losses. Moving the rim seal away from the blade-leading edges reduced the pressure asymmetry at the rim seal and increased the flow uniformity of the leakage air. However, this led to an increased cross-passage flow (more negative skew) and higher losses at all but lowest leakage fractions. The results presented in this paper highlight the fact that there may not be an optimum rim seal solution that would offer an improvement for the full range of leakage fractions and that, for different rim sealing flows, there may be a different optimum geometiy. In addition, rotor disk movements in radial and axial directions at various off-design conditions should be considered as a part of the design process. Based on the presented results, it may be of a benefit to the turbine designer to consider rotor disk designs that would be more biased towards the upstream and outward disk movements, which would result in tightening of the seal clearances and avoidance of a backward-facing annulus step.

Meander-Like Shape Optimization of the Stator-Rotor Platform Cavity

“…The correlation from Churchill and Ozoe [26], Eqn. (10), was used to estimate the laminar NuD with n set to 10. Graetz number (Gz) was computed using the hydraulic diameter of each station in Fig.…”

“…Popović and Hodson [9] investigated the effect of changing the overlap of the rim seal geometry on sealing effectiveness and the effect on the passage vortex using a linear experimental rig. In 2013, Popović and Hodson [10] experimentally tested a variety of seal designs that are similar to what is currently used in industry. They discovered that an inclined ejection does not result in a strong leakage vortex.…”

Heat Transfer and Film Cooling on a Contoured Blade Endwall With Platform Gap Leakage

“…Thrift et al [5] Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF showed a dramatic difference in the development of the horseshoe vortex upstream of a vane as a function of slot orientation angle, with a 45 deg slot essentially eliminating the development of the vortex and providing almost 150% improvement in the coolant coverage. A series of studies [6][7][8] investigated the leakage from realistic rim seals with representative tangential velocity. Their work showed the importance of a recirculating vortex in the upstream cavity on aerodynamic loss generation, with the best performance when the vortex was moved further into the rim seal, and the blade-vane overlap was made as smooth as possible.…”

Numerical Research on Flow Characteristics at High Radii of Rim Seals with Different Geometric Structures

“…In 1988, Phadke and Owen [13] studied seven sealing structures with different complexity levels, including a radial sealing structure and an axial sealing structure, and obtained the correlations of the minimum sealing flow. In 2012, Popovic and Howard et al [14] studied the characteristics of the same sealing structure by altering the parameters of its geometry. Subsequently, Mi-Ae Moon [15] added a fin based on this Ivan geometry, and the results showed that the fin could significantly block the ingress fluid.…”